1. Field of the Invention
The present invention relates to a golf putter, and more specifically to improvements in a putter shaft.
2. Description of the Related Art
A golf putter is generally required to have characteristics such as the following:
(1) The golf putter should have a sufficient weight so as not to be easily moved by slight movements of small muscles such as those in the fingers or wrists;
(2) The golf putter should have the moment of inertia by which a golf player can feel the weight thereof which is controllable during a putting stroke;
(3) When a putting stroke is executed, during the downswing, the putter shaft should flex gradually and evenly from the butt (at the hand) to the putter head in a flexing direction wherein the putter head swings down slower, and during the subsequent follow-though, the putter shaft should return gradually and evenly from the butt to the putter head (namely, the putter shaft should flex smoothly and subsequently return to the original shape smoothly with constant rhythm);
(4) The putter shaft should be capable of applying proper forward rotation (over spin) to the ball easily;
(5) The putter shaft should always convey a player's movement to the ball in the same way; and
(6) The putter shaft should be small in energy loss caused by the striking (hitting) point of the putter head.
In these characteristics, the sufficient weight in the above characteristic (1) and the moment of inertia in the above characteristic (2) are comparatively easy to set up, while each of the above characteristics (5) and (6) is almost equivalent to a characteristic given to the putter shaft when isotropy (the quality of exhibiting properties with the same values when measured along axes in all directions) is given to the putter shaft. The putter shaft made of an isotropic material can reduce the shake of the putter head no matter which point of the putter head the ball hits. Namely, no matter which direction tension is applied to the putter shaft from, the putter shaft made of an isotropic material can support the putter head with substantially the same reaction. Although isotropy depends on the quality of the material (steel being an isotropic material), a carbon shaft which consists of CFRP (carbon fiber reinforced plastic) cannot be said to have isotropy unless it uses a triaxial woven fabric.
On the other hand, the above characteristics (3) and (4) are closely related to each other. Specifically, if the shaft of a golf putter has the above characteristic (3), proper forward rotation (over spin) can be applied to the ball by hitting the ball while stroking it from bottom up with the golf putter; reverse rotation is applied to the ball if the ball is hit from top down with the golf putter. In this connection, the ball to which forward rotation is given from the beginning tends to roll well and proceeds in a desired direction, whereas the ball to which reverse rotation is given from the beginning tends not to roll well nor proceed in a desired direction. This is because the ball to which reverse rotation is applied at a putting stroke by the golf putter normally moves forward while sliding along a putting green at the beginning, and thereafter the rotational speed of the ball gradually decreases due to the resistance of the grass on the putting green, and finally the ball first stops rotating reversely to thereafter start rotating forward. This change of rotational direction of the ball from reverse to forward causes the ball to lose the inertial force thereof, and the aiming accuracy is lost in that process. For instance, a serial-stepped steel putter shaft does not flex smoothly during a putting stroke, and accordingly cannot have the above characteristics (3) and (4).